Controlling the safe and proper transfer of flammable fluids when loading transportation vehicles such as tanker trucks has long been a concern in the petroleum industry. In recent years, safety devices have been implemented on tanker trucks that prevent fluid transfer from a loading terminal to the truck if certain unsafe conditions surrounding the transfer exist. These devices use detection equipment to determine if all of the safety precautions have been taken and prevent fluid flow if they have not. The prevention of fluid flow is controlled electrically, by closing a valve in a fluid transfer conduit, or by disabling a pump that is responsible for transferring the fluid to the tanker.
Presented in FIG. 1a is a schematic representation of a tanker truck 100 that has multiple fluid containment compartments 102. The number of compartments can vary from one tanker truck to another. In the United States, tanker trucks typically have four to five compartments, and in Europe, tanker trucks can have up to sixteen compartments. Consequently, each compartment 102 can be filled with a different type of fluid; this provides for the transit of a variety of fluid types in a single truckload. Each compartment can have a total volume that differs from one another. Moreover, each compartment can have some remaining fluid, the amount of which can differ from one compartment to another. As a result, the amount of fluid required for filling each compartment 102 can be different.
To prevent overfilling of the compartments 102, an overfill sensor 104 is located in each compartment. In general, the sensor is located near the top of the compartment to detect if the fluid has reached a certain threshold level. The threshold level can depend on the size of the compartment or on the specific type of fluid that is being transferred into the compartment. The sensor 104 of each compartment 102 is connected to a connection socket 106 by which the truck is connected to a controller 108 that is located at the pumping site. The controller 108 receives signals from various sensors on the truck and stops the filling of the tanker truck 100 when a hazardous condition is detected, such as when one of the overfill sensors indicates that the fluid in its compartment has reached the threshold level.
There are several types of sensors and various ways of connecting the sensors 104 to the connection socket 106 of the controller 108. For example, one sensor type has two wires whereby the sensors can each be independently connected to the connection socket. This provides a simple way for the controller to monitor the sensors since, when a sensor detects an overfill condition, the controller can easily detect which sensor has been triggered and, therefore, which compartment is full. However, since each sensor is independently connected to the connection socket, a sufficient number of available pins are required on the connection socket for connecting the sensors all at once. This can be particularly problematic for trucks having a large amount of compartments and thereby requiring a large amount of sensors to be connected, since the number of pins provided on a standard connection socket may not be sufficient.
In another example, an alternate sensor type has a connector with five wires whereby the overfill sensors are connected together in series in a “daisy chain.” That is, a detection signal from a first sensor is passed to a subsequent sensor and so on to the end of the sensor chain, the detection signal from the last sensor being returned to the controller. If there is an overfill condition in any one of the compartments, the sensor for that compartment will not output the detection signal, the chain is broken and the controller does not receive the detection signal. The absence of a detection signal at the output of the daisy chain thereby indicates to the controller the presence of an overfill condition in one of the compartments. Irrespective of the number of sensors connected to the controller, the number of pins required by the daisy chained sensors on the connection socket is always the same, so the number of truck compartments that may be monitored is not limited by the socket. However, the monitoring process of the controller is more complex, since it is difficult to identify which of the daisy chained sensors is detecting an overfill condition. Moreover, unlike with the two wire sensor, malfunctioning sensors can very easily be bypassed, leaving the compartment of the sensor unprotected from possible overfills.
Sensors 104 of each compartment 102 that are daisy chained together are connected so that the output of one sensor is the input of the next sensor. A pulse generator on the controller on the loading terminal sends a pulse to the input of the first sensor 104 and the controller 106 looks for a pulse return at the output of the last sensor 104. If the return pulse is detected, the controller 106 determines that all sensors are connected and that none of the compartments are overfilled. However, if there is no return pulse detected, the controller 106 determines that either at least one sensor is disconnected or that, in at least one compartment, the fluid has reached its overfill level, and therefore terminates the filling process for all compartments.
One problem with sensors connected in series is that a malfunctioning sensor can easily be bypassed without the controller detecting the bypass. Presented in FIG. 1b is a schematic illustration of three sensors 104 that are daisy chained together, the pulse output 206 of a sensor being connected to the pulse input 204 of the next sensor. It is possible to bypass a malfunctioning sensor 110 by connecting the pulse output of the previous sensor to the pulse input of the next sensor, such as illustrated in FIG. 1c. Since the bypassed sensor no longer has an effect on the propagation of the detection pulse, there is a possibility for the filling operations to continue, causing an overfill and spill. This creates a potentially dangerous situation, where spillage of fluids such as hazardous or flammable fluids can cause fatal accidents.
It is also known to provide a second checking mechanism that uses a Truck Identification Module (TIM) to assign a unique serial number to a vehicle. The TIM, once attached to a specific vehicle, associates a unique ID, i.e., a Truck ID (TID) that can be read by several different systems. The TID is used for several purposes by the terminal automation system and rack controller.
As known, the TIM and associated TID can be used to validate a vehicle's authorization to load in an unmanned terminal. In such a system, the rack equipment (or terminal automation system) maintains a list of authorized trucks, by TID, that are approved to load at that loading bay (Rack). If an unauthorized vehicle attempts to load, the system denies loading and records the attempt for logging or data collection purposes.
In addition, the TID can be used for verifying fuel type access. Here, a loading Rack checks an incoming vehicle's TID to validate that the fuel they are attempting to load is approved for that vehicle. Where a loading facility often has multiple loading racks, one might be for dispensing diesel fuel, another for gasoline and yet another for aviation fuel as found at a military base or airport. The use of the TID for fuel verification prevents a vehicle from taking on the wrong fuel type
Currently, the fact that every TID is unique requires that every time a vehicle, i.e., a truck, is added to, or transferred out of, a fleet of vehicles, the TID must be entered or deleted from every rack controller that the vehicle might visit. In many instances, this involves a field visit to the rack where the TID has to be manually entered into the controller. In large and dynamic fleets this reprogramming of racks becomes burdensome. For example, in the case of military bases, a vehicle may change bases and or fuel types frequently. Such reallocation necessitates the reprogramming of controllers to delete or add new TIDs from the racks—a costly and inefficient process.